Published by Utah State University Extension and Utah Plant Pest Diagnostic Laboratory ENT-149-11 September 2011 Eriophyid Mites bud, blister, gall, and rust mites Ryan S. Davis, Arthropod Diagnostician and Taun Beddes, Cache County Horticulture Agent WHAT YOU SHOULD KNOW • Eriophyid mites cannot be seen without a 20x hand lens or greater magnification. • Eriophyid mites seldom cause serious injury or stress to plants; damage is normally aesthetic. • Damage from eriophyid mites usually consists of leaf galls, bud or flower galls, blisters, scabbing, and deformities of leaves, stems, buds, and flowers. • Control techniques include pruning, plant removal, insecticidal soap, horticultural oils, predatory mites, and broad-spectrum insecticides and miticides. Fig. 2. Microscopic view of an eriophyid mite (Aceria INTRODUCTION anthocoptes).2 Eriophyid mites are translucent, cigar-shaped microscopic mites that cause deformities on many plants species. described from around the world with many species still These mites are noticed when their feeding causes abnor- undescribed. Needless to say, you are likely to encounter malities of plant tissues such as erineum, galls, brooms, these mites some time in your gardening future. leaf curling, blisters, rusts, silvering, fruit rusetting, and de- formed buds, catkins, fruits, etc. Fortunately, these mites rarely cause serious harm to plants, and control is seldom needed. In fact, eriophyid mites can serve as an alterna- GENERAL BIOLOGY tive food source for predatory mites when their primary Family Name: Eriophyidae food source is absent. In that way, eriophyid mites can actually help reduce outbreaks of spider mites and other Range: Worldwide insects on which predatory spider mites feed, by allow- Hosts: Some mites are host specific, while others attack ing predatory mites to survive in the absence of their many plant, tree, and shrub species (Table 2). primary food. There are 1,859 species of eriophyid mites Identification of Adult:Nearly invisible to the unaided eye (1/100” in length), cylindrical/cigar-shaped, tapering from head to rear, and translucent white (Fig. 1). Unlike most mites, eriophyids only have 4 legs located near the head. Life History: Mites generally overwinter as fertilized adult females under bud scales, or protected sites on or near the host plant, and emerge at bud break in spring. Both males and females are present throughout the growing season. Reproduction is continuous, with generations completed every 2-3 weeks; overlapping generations are present. Key Habits: Overwintering females emerge from under budscales and other protected sites to lay eggs and feed on new foliage when buds begin to break in the spring. This time is most adventitious for insecticide applications. Fig. 1. Citrus rust mite (Phyllocoptruta oleivora).1 Some may transmit viruses that can deform plants or GENERAL BIOLOGY CONTINUED cause economic losses to various crops. Damage description: Below are pictures of symptoms caused by eriophyid mites categorized by plant part. Fig. 9. Cottonwood catkin gall mite (Eriophyes newesse- Fig. 10. Ash flower gall mite (Eriophyes fraxiniflora).1 gi).3 Fig. 3. Galls caused by boxelder pouchgall mite (Eriophy- Fig. 4. Leaf blisters on pear caused by pearleaf blister es negundi).3 mite (Phytoptus pyri).4 Fig. 11. Hackberry witches broom caused by Eriophyes Fig. 12. Example of a stem gall mite (Aceria sp.) on celtis.3 maple.8 Fig. 5. Erineum on Rocky Mountain Maple caused by Eri- Fig. 6. Fingergalls on chokecherry caused by Phytoptus ophyes calaceris.5 emarginate.4 Fig. 13. Poplar bud gall caused by Eriophyes parapopuli.3 Fig. 14. Damage caused by rose rosette virus transmitted by Phyllocoptes fructiphilus.4 PHOTO CREDITS 1. Texas A&M University, http://cookislands.bishopmuseum.org/species.asp?i 6. Clark, J.C. University of California Statewide IPM Project. d=9294. 7. Solomon, J. USDA Forest Service. Bugwood.org. 8. Csoka, G. Hungary Forest Research Institute. Bugwood.org. 2. Eric Erbe, USDA Agricultural Research Service, Bugwood.org. 3. Whitney Cranshaw, Colorado State University, Bugwood.org. Fig. 7. Bronzing of pear leaves caused by pear rust mite Fig. 8. Russeting of pear fruit by pear rust mite (Epitrimerus 4. Keifer, H.H., Baker, E.W., Kono, T., Delfinado, M., and Styer, W.E. An (Epitrimerus pyri).6 pyri).6 Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites. 5. Ciesla, W.M. Forest Health International. Bugwood.org. requires full coverage of foliage (top and bottom) CONTROL to be effective. Frequent applications are needed, eriophyid mite damage occurs on many plant species but may cause plant stress if used too often (inhibits and often does not impact long term health. Because photosynthesis). COMMON ERIOPHYID MITES AFFECTING PLANTS IN UTAH of this, chemical pesticides should not be considered a • Sulfur: Sulfur has long been used for mite control. Common Name Scientific Name Host Plants Damage Description primary management option. Full coverage is necessary for control. Do not apply tomato russet mite Aculops lycopersici tomato, nightshade plants new infestations turn lower stems and leaves brown, when temperatures exceed 90°F, or during periods of (Solanaceae) eventually withering; rusetting of tomato fruit; death high humidity. Non-Chemical Control • Neem oil: Azadirachtin (group unknown) is a bo- honeylocust rust mite Aculops spp. honeylocust feeding on undersides of leaves causes bronzing that is Cultural control practices that modify the growing envi- tanical insect growth regulator acquired from neem visible by late summer ronment can reduce the occurrence of unwanted pests. trees. peach silver mite Aculus cornutus peach, nectarine, almond silvering of leaves in late summer before leaf drop • Pesticide avoidance: Overuse of insecticides and • Predatory mites: Naturally occurring predatory willow pouchgall mite Aculops tetanothrix willow 2-3 mm diameter irregular and beadlike galls usually miticides can eliminate natural predators, and can mites often feed on Eriophyid mites and can keep located near the leaf midrib or between veins; gall color lead to pest resistance, making long-term control populations at tolerable levels. Avoid the use of is pink to red-purple to yellow and ranges from fuzzy, rough, to smooth; galls may cover whole leaf difficult. broad-spectrum insecticides to preserve predatory mites. Low or extinct populations of predatory mites apple rust mite Aculus schlechtendali apple injured terminal growth; lengthwise leaf curl; fruit ruset- • Monitor/scout: Periodic examination of plant mate- my be supplemented with predatory mites available ting rial reveal Eriophyid populations before they increase for order. One good option for hot arid regions is privet rust mite Asculus ligustri privet scratched appearance on top of leaves turning brown; to damaging numbers. Galendromus occidentalis (western predatory mite). leaf curl on young leaves • Plant selection: Use plants that are less susceptible Other species of predatory mites are available, but grape erineum mite Colomerus vitis grape deformation of bud clusters; felty erineum on lower leaf to eriophyid mites, and that are adapted to Utah’s work best in humid conditions, such as in a green- surface followed by blister-like swellings on upper leaf arid climate; contact your local USU Extension office house. Rocky Mountain Maple Eriophyes calaceris Rocky Mountain Maple greenish yellow to pink, crimson, or purple-red erineum for recommendations. Make sure plants or planting erineum mite on upper leaf surface, usually missing the major veins material you select are free from eriophyid mites. Insecticides and Miticides (Fig. 5) • Prune: Remove infested leaves or branches and hackberry mite Eriophyes celtis hackberry thin, short, stunted, and tightly bunched twigs resulting Table 1 contains an abbreviated list of active ingredients remove from the property. in witches’ brooms (Fig. 11) effective against Eriophyid mites. Make sure the host ash flowergall mite Eriophyes fraxiniflora ash infloresence gall (Fig. 10) • Plant removal: Heavily infested plants such as toma- plant is listed on product label you choose. toes and wheat, may need to be removed to reduce boxelder pouchgall mite Eriophyes negundi boxelder pouch-like galls on upper leaf surface created by inden- • When using pesticides, rotate the chemical group the spread of mites. Some mites have secondary tations on the underside of leaves, filled with fine white on a yearly basis to avoid insect resistance. Chemi- hairs-galls are mostly solitary, located between veins host plants, so removal of host weeds minimizes cal groups are listed in Table 1. sources of re-infestation. cottonwood catkin gall mite Eriophyes newessegi poplar (Populus spp.) grape-like growths/distortions of catkins; affected cat- • For gall-forming mites, once visible damage such as kins remain on tree until mid summer (Fig. 9) galls are observed, it is often too late to treat during poplar budgall mite Eriophyes parapopuli poplar irregular, asymmetrical, bumpy, solid mass of fleshy Chemical Control that growing season. swelling of the bud (Fig. 13) If severe infestations are causing major aesthetic dam- wheat curl mite/bulb mite Eriophyes tulipae barley, oats, corn, wheat, Poa leaf curling; red-streaked corn; leaf margin curling; age, tree stress, or crop economic loss, insecticides/miti- spp., Agropyron spp., foxtail brown blistering on bulbs; can transmit wheat streak cides may be necessary. Consider reduced-risk pesticides Active Ingredient